In a power unit in which an internal combustion engine and a transmission are united with each other, a multiplicity of oil passages are formed to conduct oil to supplied parts supplied with the oil, such as lubricated parts, e.g., sliding parts in the power unit, and a hydraulic operating device using the oil as a working fluid. In the case where a component member of the power unit is used as an oil passage forming member and a bent oil passage is formed in the oil passage forming member, usually, a first hole and a second hole respectively constituting parts of the oil passage are made to intersect, thereby forming a bent passage part. In this instance, one of the first hole and the second hole is formed by drilling from an outer surface of the oil passage forming member, and, after the drilling, the aperture end part of one of the first and second holes which opens at the outer surface is closed with a plug. See, for example, Japanese Patent Laid-open No. Hei 6-117327.
In addition, an oil passage forming member is known that is fitted with a hydraulic pressure sensor for detecting the hydraulic pressure in the oil passage formed in the oil passage forming member.
Further, a system is known wherein the transmission of the power unit provided with the oil passage forming member is composed of a swash plate type hydrostatic continuously variable transmission. See, for example, Japanese Patent Laid-open No. 2005-248838 and Japanese Patent Laid-open No. 2005-263143.
Meanwhile, the hydraulic pressure sensor for detecting the supplying condition or hydraulic pressure condition of the oil supplied to the supplied part is desirably disposed as close as possible to the supplied part, in order to monitor more accurately the hydraulic pressure condition at the supplied part.
However, since the hydraulic pressure sensor must front on the oil passage, it may be necessary, for enabling the hydraulic pressure sensor to detect the hydraulic pressure at a preferable position in the oil passage, that a mounting hole which communicates with the oil passage and in which to fit the hydraulic pressure sensor be formed in the oil passage forming member. However, the formation of such a mounting hole needs special machining and, accordingly, leads to an increase in the cost of the oil passage forming member.
In addition, the plug used to close the aperture end part of the oil passage would itself increase the number of component parts, and needs a plug mounting step, thereby also causing an increase in cost.